novel propulsion for travel with in the solar system

[udtsith]

Could you make a solar sail that derives it's energy from the decay of a radioactive element such as plutonium, uranium, or palonium? I understand that such elements radiate in all directions but if you had a 1 kg sphere of it attached to a boon which was attached to a reflective sail (e.g. aluminum) would you not be able to harness the total momentum generated by the alpha, beta, or gamma particles? If the alpha particles are absorbed rather than reflected then...couldn't you encase the radioactive element in a lead casing, allowing it to heat and emit it's energy via infrared to the solar sail? I understand that gamma will likely sail on through but most of the energy released in decay is from alpha particles which are easily blocked. My estimate is that you could get up to 1/1000th the speed of light from the energy that is released over a 100 day decay of palonium (140 W/gram). This wouldn't be worthwhile for interstellar travel but you could zip around the solar system quite nicely. The thrust should be about 50X that of the Sun's radiation pressure near earth but if you need more you could simply increase the size of the 1Kg sample.

[novaderrik]

if you were going to direct the radiation in one direction, then why even bother with the sail- it would be a bit like using a box fan on the back of your sailboat to blow air onto the sail for propulsion.

[Paul Wally]

Could you make a solar sail that derives it's energy from the decay of a radioactive element such as plutonium, uranium, or palonium? I understand that such elements radiate in all directions but if you had a 1 kg sphere of it attached to a boon which was attached to a reflective sail (e.g. aluminum) would you not be able to harness the total momentum generated by the alpha, beta, or gamma particles? If the alpha particles are absorbed rather than reflected then...couldn't you encase the radioactive element in a lead casing, allowing it to heat and emit it's energy via infrared to the solar sail? I understand that gamma will likely sail on through but most of the energy released in decay is from alpha particles which are easily blocked. My estimate is that you could get up to 1/1000th the speed of light from the energy that is released over a 100 day decay of palonium (140 W/gram). This wouldn't be worthwhile for interstellar travel but you could zip around the solar system quite nicely. The thrust should be about 50X that of the Sun's radiation pressure near earth but if you need more you could simply increase the size of the 1Kg sample.

I think you have to take into account Newton's 3rd Law here. Ideally you don't want to absorb anything with a lead casing, rather you would want to reflect as much of the radiation in the direction opposite to which you want to travel. For this you will need something like a parabolic reflector, rather than a sail, with the radiation source at its focus. This will work if you can design such reflective material for the dish.

[cjameshuff]

http://en.wikipedia.org/wiki/Fission_sail